1. Field of the Invention
The present invention relates generally to apparatus and methods for introducing devices to target locations within body lumens and cavities. In particular, the present invention relates to introducing catheters and methods which are used to provide large-diameter access lumens to target locations disposed along or at the distal end of tortuous paths.
Introducer sheaths and catheters are commonly used to provide endoluminal and/or percutaneous access to remote target locations in a variety of medical procedures, including intravascular procedures, laparoscopic procedures, and other minimally invasive procedures. Of specific interest to the present invention, the endovascular placement of vascular grafts for the treatment of abdominal aortic aneurysms has been proposed, where the graft may be inserted into the aorta via an antegrade or retrograde arterial approach. Such endovascular graft placement will require the use of a relatively large graft placement catheter, typically having an outer diameter in the range from 4 mm to 10 mm. Such large placement catheters will require correspondingly large introducing catheters or sheaths, typically having an internal lumen diameter which is at least slightly larger than the outer diameter of the placement catheter. The placement and use of such large-diameter introducing catheters or sheaths will be problematic in several respects.
In particular, the antegrade path into the subclavian artery, through the aortic arch, and into the thoracic aorta is quite tortuous. While the path can be readily negotiated by conventional intravascular guide wires, such guide wires have very small diameters and are not sufficiently strong to permit introduction of a large diameter introducing sheaths thereover. To overcome this problem, it would be possible to employ an introducing sheath having an integral steering mechanism. Such sheaths could be introduced around even the very tight curves encountered in the transition from the subclavian artery to the aortic arch. The incorporation of a steering mechanism, however, necessarily reduces the lumen area of the sheath which is ultimately available for accommodating the graft-placement catheter.
Other problems which arise when introducing sheaths are used for aortic access include the design of the hemostasis valve. The hemostasis valve must be able to accommodate very small devices, such as guide wires, as well as the very large graft-placement catheter. The body of the sheath must have a very thin wall (to maximize available area in the access lumen), and a very smooth lumen to permit the passage of the graft-placement catheters without sticking or constriction of the catheter. Additionally, placement of vascular grafts through an introducing sheath located in the abdominal aorta is further made difficult by the relatively high blood flow rate through the aorta. Moreover, the ability to anchor the vascular graft within the aorta and/or adjoining iliac arteries can be problematic and require additional devices which are difficult to provide through the limited area of the access lumen.
For these reasons, it would be desirable to provide improved catheter introducing systems and methods, including catheter sheaths, sheath steering mechanisms, hemostasis valves, and the like, which overcome at least some of the deficiencies described above. The introducing sheaths should have a large lumen diameter, typically being at least 4 mm, to accommodate large diameter graft-placement catheters, should have good hoop strength to avoid kinking or collapse of the sheath when bent around tight curves, and should have good column and tensile strengths to avoid deformation when the graft-placement catheter is passed through the lumen. The sheath steering mechanisms should provide for a high degree of lateral deflection at the distal end of the sheath but should not take up lumen area which is necessary for subsequent passage of large diameter catheters. The hemostasis valves should be able to accommodate both small diameter devices, such as guide wires, and the large diameter catheters while still maintaining a tight seal around the catheter to prevent leakage.
2. Description of the Background Art
A steerable sleeve for use in combination with a flexible catheter is described in DE 39 20 707. U.S. Pat. No. 4,976,688 shows a steerable sheath structure. European Patent Application 488 322 shows a tubular device having a variable curvature controlled by differential pressure. Other catheter- and device-steering mechanisms are described in U.S. Pat. Nos. 5,109,830; 5,098,412; 5,019,040; 4,983,165; 4,066,070; and 3,941,119.
A large-diameter introducer sheath having metal-ribbon reinforcement and a proximal hemostasis valve is described in U.S. Pat. No. 5,180,376. Devices covered by the ""376 patent are sold by Arrow International, Inc., Reading, Pa. 19605, under the name super Arrow Flex(trademark) percutaneous sheath introducer set with integral side port/hemostasis valve. Other reinforced tubular catheter designs are described in U.S. Pat. Nos. 5,279,596; 5,275,152; 5,226,899; 5,221,270; 5,221,255; 5,069,217; 4,985,022; and 4,411,655.
U.S. Pat. No. 5,207,656, discloses a hemostasis valve having a foam member for sealing against a catheter passed therethrough. The foam member has a lubricant absorbed in an open-cell foam structure. U.S. Pat. No. 4,475,548, discloses a foam sealing member for use in an endotracheal tube. European patent application 567,141 describes a trocar valve assembly which may include a flexibly resilient material for reception of an instrument passed through the valve. Other hemostasis and similar valve structures are described in U.S. Pat. Nos. 5,338,313; 5,300,034; 5,279,597; 5,242,425; 5,222,948; 5,215,537; 5,167,636; 5,127,626; 5,104,389; and 4,177,814.
The present invention provides apparatus and methods for placement of a flexible introducer sheath at a target location in a body lumen or cavity. Placement of the flexible sheath is usually percutaneous, i.e., through a puncture or incision in the patient""s skin, and endoluminal i.e., through a body lumen or cavity which has been accessed through the percutaneous puncture site. An exemplary use of the apparatus and methods of the present invention is placement of a flexible sheath through the subclavian or brachial arteries, through the aortic arch, and into the abdominal aorta for the delivery of a vascular graft intended for treatment of an abdominal aneurysm. The apparatus and methods of the present invention, however, are not limited to use in such graft placement procedures and may find additional uses in a wide variety of procedures, including laparoscopic and other minimally invasive procedures where it is desired to introduce a large diameter sheath into a body cavity or lumen and subsequently steer or manipulate the distal end of the sheath to a target location within the luminal cavity.
In a first aspect of the present invention, a catheter introducing system comprises a flexible sheath having a proximal end, a distal end, and an access lumen extending therebetween. An obturator is removably received in the lumen of the flexible sheath and includes a mechanism for laterally deflecting at least a distal portion of the obturator. In this way, the distal end of the flexible sheath can be manipulated using the obturator to facilitate intravascular or other placement of the sheath. After the sheath has been introduced to the desired target location, the obturator may be withdrawn, leaving the access lumen open to receive guide wires, working catheters, and the like. Since the size of the obturator is limited only by the area of the sheath access lumen, there is sufficient available cross-sectional area for providing effective and efficient steering mechanisms. In particular, it will be possible to provide steering mechanisms which are capable of inducing small-radius deflections in the distal end of the sheath, typically as low as one cm.
In a second aspect of the present invention, a method for introducing a flexible sheath to a target location in a body lumen comprises introducing the sheath to the lumen and advancing the sheath within the lumen while laterally deflecting at least a distal portion of an obturator which is removably received in a lumen of the sheath. The obturator is removed from the sheath after the target location has been reached in order to provide the desired access lumen. Usually, the obturator will be within the sheath with its deflectable distal end axially aligned with a distal portion of the sheath having enhanced flexibility. Alternatively, the obturator could be advanced distally beyond the sheath, using the steering mechanism to reach the desired target location, with the sheath then being advanced over the obturator. The method is particularly useful for introducing the sheath into the subclavian, external carotid, axillary, or brachial arteries, through the aortic arch, and into the abdominal aorta, but can also be used for a variety of procedures as described above.
In a third aspect of the present invention, an aortic introducer catheter comprises a flexible sheath having a proximal end, a distal end, and an access lumen extending therebetween. The length between the proximal and distal ends is in the range from 30 cm to 60 cm and the lumen diameter is in the range from 4 mm to 10 mm. A hemostasis valve is secured to the proximal end of the sheath, and the aortic introducer catheter is particularly useful for providing an access lumen into the subclavian or brachial arteries, through the aortic arch, and into the abdominal aorta. The catheter preferably has a region of enhanced flexibility over a distal length in the range from 5 cm to 15 cm so that it may be utilized in combination with a steerable obturator, as described above. The aortic introducer catheter may further comprise an expandable member, typically an inflatable balloon, located at from 1 cm to 10 cm from its distal end where the expandable member can be used to partially occlude blood flow when expanded inside the aorta. The catheter may additionally or alternatively, include an expandable member, again typically an inflatable balloon, at its distal end, where the distal expandable member can be used for anchoring an aortic prosthesis by internal expansion.
In a fourth aspect, the present invention provides a catheter sheath comprising a tubular inner liner having a proximal end, a distal end, and a lumen therebetween. The inner liner will preferably be formed from a lubricous material or have its inner lumen coated with a silicone gel or other lubricating material. Flat wire helical coil is wrapped over the exterior surface of the tubular inner liner, and the coil has spaced-apart adjacent turns. Plastic coating is formed over the helical coil and penetrates into the space between the adjacent turns. The coating bonds to the inner liner to provide an integral structure having a thin wall with controlled flexibility. The sheath preferably has a region of enhanced flexibility near its distal end, where flexibility can be controlled by utilizing liner materials, plastic coating materials, or both, having lower durometers near the distal end. Alternatively, the flexibility can be controlled by utilizing different helical coil materials or by modifying the spacing between adjacent coil turns to enhance the flexibility. The catheter sheaths will also preferably have a soft tip over a distal length in the range from 2 mm to 10 mm. The soft tip will usually be free from the helical coil and may optionally be formed from a material having a lower durometer.
In a fifth aspect of the present invention, a steerable obturator is provided comprising a flexible body having a proximal end and a tapered distal end. A mechanism will be provided in the body for laterally deflecting at least a distal portion of the body. Typically, the lateral deflection mechanism will comprise a pull wire which is attached off center at the distal end of the flexible body. The pull wire can be actuated by a handle secured to the proximal end of the body. The obturator will preferably have a region of enhanced flexibility at its distal length, where the region of enhanced flexibility may comprise a series of articulated elements.
In a sixth aspect, the present invention provides a hemostasis valve comprising a housing having an interior cavity and axially aligned inlet and outlet ports. A compressible insert is disposed within the interior cavity of the housing and includes a polymeric foam body having an open axial lumen in an exterior geometry which is similar to but larger than the interior cavity in the housing. By confining the foam insert within the interior cavity of the housing, the open lumen will be closed to provide a seal between the axial lined ports of the housing. The circumference of the lumen, however, will be sufficiently large to accommodate even large diameter catheters and devices subsequently introduced through the valve. The particular advantage of this design is that the lumen in the foam insert will not be stretched or torn as the catheter is being introduced therethrough. That is, the original cross-sectional circumference of the lumen will remain even though the lumen has been collapsed by external compression. Preferably, the hemostasis valve will include a second valve element, such as a duckbill or slit disc structure to provide for hemostasis when no catheter or device is placed through the foam insert. The lumen of the foam insert will also preferably be coated with a lubricant and optionally provided with a protective layer to further guard against tearing of the foam as the catheter is passed therethrough.